1. Field of the Invention
The present invention relates to a gas lift system including a lift gas and a gas retention composition, where the composition improves gas lifting properties of the system and to methods for making and using same.
More particularly, the present invention relates to a gas lift system including a lift gas and a gas retention composition including a hydrocarbon base fluid, a viscosifying agent and optionally a foaming agent. The system is designed to be injected with or into a lift gas stream being pumped down hole and the resulting mixture of production fluids, gas lift and gas retention composition reduces a column weight increasing the amount of production fluids being transported to the surface. The injection can be at the surface or at any point down hole. The invention also relates to methods for making and using the systems of this invention.
2. Description of the Related Art
To obtain hydrocarbon fluids from a hydrocarbon bearing formation, a wellbore is drilled into the earth to intersect an area of interest within the formation. The wellbore may then be “completed” by inserting casing into the wellbore. Generally, after casing the wellbore, the casing is cemented into place by pumping cement between an outer surface of the casing and the wellbore. Alternatively, the wellbore can remain uncased, a so called “open hole wellbore”, or the wellbore can be partially cased and cemented. Regardless of the form of wellbore completion, production tubing is typically run into the wellbore primarily to convey production fluids (e.g., hydrocarbon fluids, water, etc.) from the area of interest within the wellbore to the surface.
Often, pressure within the wellbore is insufficient to cause the production fluids to naturally rise through the production tubing to the surface, requiring artificial lift techniques, especially when the production fluid include heavy crude oil. One such artificial lift technique is a sucker rod lifting system. A sucker rod lifting systems generally includes a surface drive mechanism, a sucker rod string, and a downhole positive displacement pump. Production fluids are brought to the surface by the pumping action of the downhole pump powered by the drive mechanism attached to pump via the sucker rod string.
Another artificial lift technique is a gas lift system. In a typical gas lift system, a compressed gas is injected into an annulus between an outer surface of a production tubing and an inner surface of a casing. A valve system controls the supply of the injection gas to the wellbore and allows production fluids to exit the gas lift system at the top of the well.
The production tubing typically has gas lift mandrels having gas lift valves distributed along the length the production tubing in a spaced apart configuration. The gas lift valves allow or disallow gas to flow from the annulus into the production tubing via the mandrels to control the amount and position of gas being injected into the production tubing. A production packer located at a lower end of the production tubing forces the flow of production fluids from a reservoir or zone of interest in a producing formation up through the production tubing (into its interior) instead of up through the annulus and reduces or prevents injected gas from entering the formation.
In operation, production fluids flow from the formation into the wellbore through perforations extending through the casing into the formation. Once in the wellbore, the production fluid flow into an interior of the production tubing and are conveyed to the surface. When it is desired to lift the production fluids with a gas, a compressed gas is introduced into the annulus at a controlled rate. Any of the gas lift valves which are in their opened position will allow the gas to flow into the production tubing through an opening in the gas lift mandrel to lift the production fluids to the surface, by reducing the weight of the fluid due to the injected gas. The injected gas lowers the hydrostatic pressure in the production tubing to re-establish the required pressure differential between the reservoir and the wellbore, thereby causing the production fluids to flow to the surface.
Gas lift systems are often the preferred artificial lifting systems because they have fewer moving parts than other lifting systems. Moreover, gas lift systems are useful in many well where alternatives cannot be used.
Although gas lift systems are advantageous in most applications, wells which contain heavier production fluids (such as production fluid including heavier crude oil) are often not effectively served using typical gas lift systems. When heaver crude oil is present in the production fluids, the injected gas tends to channel up the production tubing. This gas channeling causes a stratified flow up the production tubing reducing the amount of production fluids being lifted to the surface and decreasing overall well production.
Thus, there is a need in the art for a gas lift system capable of effectively lifting production fluid, especially productions fluids that include heavy crude oil, from a producing formation to a surface and capable of reducing stratification of the production fluids in the production tubing, regardless of the makeup of the production fluids.